1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To eliminate this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses a thermally-assisted magnetic recording head including a main pole, a waveguide and a plasmon generator. The main pole has an end face located in the medium facing surface, and produces a write magnetic field from this end face. The plasmon generator has an end face located in the medium facing surface. The waveguide includes a core and a cladding. In this head, the surface of the core and the surface of the plasmon generator face each other with a gap interposed therebetween. This head is configured to excite surface plasmons on the plasmon generator by using evanescent light that occurs on the surface of the core based on the light propagating through the core, and to cause near-field light to be generated from the end face of the plasmon generator based on the excited surface plasmons.
A thermally-assisted magnetic recording head including a plasmon generator causes a spot of near-field light to be formed on a recording medium by the plasmon generator. The size of the spot of near-field light will hereinafter be referred to as light spot size. It has conventionally been considered that a smaller light spot size is effective for achieving higher recording density.
On the recording medium, the spot of near-field light generates a temperature distribution such that the temperature peaks at the center of the spot, and decreases with increasing distance from the center. Magnetic recording is typically performed on a ring-shaped region on the recording medium, the region having a temperature of 400° C. to 500° C. Hereinafter, a region on the recording medium formed by a combination of the aforementioned ring-shaped region having a temperature of 400° C. to 500° C. and a region on the inner side thereof will be referred to as thermal spot. Conventionally, track width depends on the thermal spot size.
The light spot size can be reduced to the order of 50 nm by downsizing the plasmon generator or reducing the power of the laser light for use to generate near-field light. However, since the heat resulting from near-field light spreads on the recording medium by conduction, the thermal spot size becomes larger than the light spot size. It is thus difficult to sufficiently reduce track width and thereby sufficiently increase recording density with the approach of reducing the light spot size alone.
U.S. Patent Application Publication No. 2011/0170381 A1 discloses the technique to form a plasmon generator by etching a metal layer using either the main pole or a mask for use to etch the main pole. This technique suffers from the problem that if the end face of the main pole and the end face of the plasmon generator are both reduced in width in order to achieve a smaller track width, the main pole becomes unable to pass much magnetic flux, thus becoming unable to produce a write magnetic field of sufficient magnitude from the end face of the main pole.
To enhance the recording density of a magnetic recording device, perpendicular magnetic recording system is preferably used. In perpendicular magnetic recording system, a write magnetic field in a direction perpendicular to the plane of the recording medium is produced from the end face of the main pole. When employing perpendicular magnetic recording system, it is desirable, in order to increase the track density, that the distribution of strength of the write magnetic field in the track width direction be sharpened.
U.S. Pat. No. 7,068,453 B2 discloses a thermally-assisted magnetic recording head including a write pole, a magnetic shield, and an electrically resistive heater. The write pole has a pole tip located in the medium facing surface. In this head, the electrically resistive heater has a width greater than one track width. The magnetic shield includes two side shields located on opposite sides of the pole tip in the track width direction, and a trailing shield located on the trailing side of the pole tip. The pole tip is surrounded by the electrically resistive heater, the two side shields and the trailing shield.
The track width of the head disclosed in U.S. Pat. No. 7,068,453 B2 is determined by the width of the pole tip. In this head, if the width of the pole tip is reduced in order to achieve a smaller track width, the write pole becomes unable to pass much magnetic flux, and consequently becomes unable to produce a write magnetic field of sufficient magnitude from the pole tip.